The invention relates generally to pipe repair. More particularly, the invention relates to techniques for efficiently repairing a pipe with fiber-reinforced polymeric material.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Piping is omnipresent in today's society. Piping is found in a wide range of residential, commercial, and industrial applications. For example, piping may be employed in utility distribution, manufacturing processes, chemical/petrochemical transport, energy transmission, plumbing, heating and cooling, sewage systems, as well as in the recovery of spent chemicals/compounds, such as discharges of exhausted chemicals, contaminated water, and so forth. In operation, piping within facilities and over longer distances, may serve to collect, distribute, and transport water, steam, chemicals, petrochemicals, crude oil, natural gas, and a variety of other liquids, gases, and components.
Piping systems, such as pipelines, may convey utilities, energy, and chemical/petrochemical components to industrial patrons, manufacturing sites, chemical/refining facilities, commercial entities, public institutions, consumers, and so on. Undeniably, pipelines (e.g., transmission pipelines) have played a beneficial role in improving productivity in delivery of resources. Indeed, world economies depend on the capability of pipelines to transport feedstocks and products to a diverse range of customers and end-users.
Peak construction of pipelines (e.g., gas and liquid petroleum pipelines) occurred 30-40 years ago, with a majority of these pipelines, including many constructed prior to World War II, still in service. As a result of their age, maintaining the integrity of the aging pipeline infrastructures is costly. Annual costs attributable to mitigating pipeline corrosion and other pipeline failures, potential failures, and anomalies, are in the billions of dollars. Economic considerations of pipeline repair may include labor, material, equipment requirements, available capital, economic return, repair life, pipeline downtime, and so forth. As expected, the economics of pipeline repair can have a significant impact on pipeline productivity.
Pipe failures and damage may be caused by mechanical harm, corrosion, erosion, damaged coatings, failing insulation, adverse operating conditions, weather, and so on. Internal erosion, for example, may occur due to the flow of the contents through the pipeline. Such erosion may be exacerbated by centrifugal forces associated with changes in the direction of the flow path. In regard to corrosion, the external surface of piping may be exposed to corrosive soil or above-ground corrosive environments, and the internal surface of piping may be exposed to corrosive contents. Significantly, erosion, corrosion, and other damage may reduce the wall thickness of the pipe and thus reduce the pressure rating or pressure-holding capacity of the pipe or pipeline. Accordingly, the operations and maintenance personnel of pipeline companies (e.g., gas transmission companies) may determine if a failure or an area of potential failure discovered in a pipeline should be repaired, if a section of the pipe should be replaced, or if the pipeline should be abandoned.
In evaluating repair decisions, pipeline operators and service providers typically consider the pipeline downtime, pipe specifications, the pipe area to be repaired, buried conditions, the above-ground environment, the contents of the piping or pipeline, pipeline operating conditions, and the like. Of course, the pipeline operators and service providers should accommodate regulatory constraints, appropriate industry standards, manufacturer recommendations, and so on. Moreover, the maintenance approach ultimately selected may involve repair of a leak or other failure, or the preemptive repair of a pipe area prior to failure (e.g., leak, rupture, etc.) of the pipeline. Finally, in an effort to maintain pipeline integrity while being mindful of costs, the environment, regulatory constraints, and so on, the pipeline operators and service providers typically assess the maintenance, replacement, and repair of piping/pipelines based on available engineering alternatives and the economic impact of those alternatives. In the case of a repair, several technologies, application techniques, and materials are available.
Common repair technologies employ metal sleeves that are disposed about a section of a pipe to reinforce the pipe. Both welded sleeves and non-welded (mechanical) sleeves may be installed over varying lengths and diameters of piping to repair pipe leaks and other failures. Also, sleeves may preemptively repair potential pipe failures, reinforce pipe areas of internal and external corrosion, upgrade the pressure rating of the piping, and so forth. In general, established sleeve techniques, whether utilizing sleeves welded in place around the pipe, or employing sleeves mechanically secured to the pipe without welding, offer the advantage of being familiar repair approaches in the industry. In the repair of pipelines, operators, engineers, and craftsman are accustomed to working with welded fittings for welded sleeves, as well as with mechanical devices and clamps for non-welded sleeves. Unfortunately, the training of personnel in the suitable mechanical and welding techniques is extensive for proper installation of the sleeves. Further, non-welded and welded sleeve repair of pipelines may result in embrittlement and residual stresses at the point of repair on the pipeline.
For welded sleeves, the sleeves may be welded around the pipe to be repaired, encasing the pipe segment to be reinforced. The mating edges of the sleeve halves may be welded to each other, and the ends of the erected sleeve welded to the pipe, to seal and secure the welded sleeve to the pipe. It should be emphasized that a variety of welding configurations other than the generic approach described above may be employed in installing the welded sleeve. Costs associated with welding repairs, including welded-sleeve repairs (e.g., on high-pressure transmission pipelines), may be attributed to the use of highly-skilled welders, the shutdown and deinventory of the pipeline, and the shutdown of associated manufacturing facilities, chemical/petrochemical processes, and so on.
Generally, it is desirable from an operating cost standpoint to repair piping while the pipeline remains in service, thus eliminating costly downtime. Repair techniques that avoid welding or cutting of the pipe, for example, may make it feasible to maintain the pipeline in service during the repair and thus avoid the costs associated with pipeline downtime. It should be emphasized that a shutdown of a pipeline for repair can potentially force the shutdown of upstream and downstream facilities, resulting in lost production, lost sales, shutdown and startup costs, and so forth.
Non-welded sleeves address this concern, because they generally do not require welding or cutting. Non-welded reinforcement sleeves are mechanically coupled to the pipe section to be repaired. In other words, these non-welded sleeves (also called mechanical sleeves) may be positioned and secured to the pipe by clamps, bolts, and so on. Regrettably, the use of non-welded sleeves may require exotic mechanical techniques to adequately secure the repair and pipe pressure rating, and thus may be more cumbersome and complicated than welding techniques. As a result, pipe repair with non-welded sleeves may be more expensive than repair with welded sleeves. However, repair with non-welded sleeves may advantageously avoid welding at the on-site repair, such as in pipeline areas and in chemical/petrochemical process areas, for example. Further, as indicated, non-welding approaches generally permit uninterrupted operation of the pipeline. On the other hand, in certain configurations for non-welded (mechanical) sleeves, the pipeline may be deinventoried if significant mechanical force is to be applied to the pipe or because of other factors during installation of the non-welded sleeve.
Unfortunately, the special case of repair of piping elbows, piping tees, pipeline bends, and so on, is problematic for both welded and mechanical (non-welded) sleeves due to the difficultly of placing a rigid metal sleeve around the curved pipe bend to be repaired. Further, the rigid metal sleeves may be unable to make adequate contact at the pipeline bends, and thus be unable to reinforce the stressed points that typically exist at the pipeline bends. Furthermore, it may be may be difficult to appropriately match the radius of curvatures of the outer metal sleeve and the pipeline elbow or bend. To avoid these problems with installing sleeves at pipeline bends, a weld filler metal (in lieu of a sleeve) may be deposited on the bend (e.g., in a cavity of an anomaly) but such welded filler repairs are generally appropriate only for limited ranges of pipeline operating pressures and wall thicknesses.
As can be seen from the discussion in the paragraphs above, a variety of challenges exist with welded and non-welded (mechanical) sleeves. On the whole, these established techniques of using reinforcement sleeves, whether welded or non-welded, tend to be costly, require highly skilled labor, result in increased pipe stresses, and increase the need to interrupt pipeline service. A need exists for improved techniques of pipe repair.
In response to the problems and challenges associated with the conventional approaches of welded and non-welded sleeves in the repair of both straight pipe and pipe bends, new technologies have emerged that involve coatings and the use of high-strength plastics, fiber-reinforced plastics, composite materials, and the like. Such polymeric repairs may reduce costs and provide for less embrittlement and residual stresses of than traditional welded and mechanical sleeves. Furthermore, polymeric composites, for example, generally do not oxidize and, consequently, may arrest further external corrosion of the treated area of the pipeline. Moreover, as a result of the growing using of composite repair systems, particularly in the oil and gas transportation industry, the American Society of Mechanical Engineers (ASME) is currently in the process of setting standards for non-metallic wrap technology including development of a new post-construction repair standard. Currently, a relatively new ASME standard (ASME PCC-2) specifies that several material properties of the repair system are to be measured and evaluated.
It should be noted that resin alone (without reinforcing materials) typically does not provide adequate strength for pipe repair, especially in the repair of medium and high pressure pipelines. Accordingly, in general, polymer repair systems are based on a matrix composite fabric with epoxy materials and other resins, creating a monolithic structure around the damaged pipe. In general, a variety of fibers, polymers, resins, pre-polymers, adhesives, and other components may be used to form a composite material structure around the damaged portion of the pipe. In particular, composite repair systems typically employ glass fibers and offer the potential to reduce repair costs of corroded pipes by avoiding costly mechanical sleeves, welding, and downtime.
As discussed below, however, fabrication of these composite repairs tends to be labor intensive. For example, each layer of the fiber is wetted with dripping resin prior to wrapping the fiber around the pipe. Several layers of fiber and resin (also referred to herein as polymer) are methodically applied by hand one layer at a time, with the fibers slowly and carefully pre-wetted in resin prior to the application of each fiber layer. For example, the fiber (e.g., fiber tape) may be pulled through a bath of polymer (e.g., epoxy resin) as the fiber is cumbersomely applied to the pipe. Such tedious handling and open installations pose environmental and application challenges, increased handling of resin chemicals and solvents, increased labor time, and the like.
In addition, as appreciated by those of ordinary skill in the art, the worker should be aware of the resin pot life (i.e., resin set-up time in minutes or hours) where the viscosity of the resin significantly increases as the pot life expires, making it difficult to properly apply the resin to the fiber, and to effectively mold and form the polymer resin composite. The resin pot life should not be confused with the resin cure time which is the time for the resin to form a cross-linked thermoset, typically occurring a day or several days later. The pot life (and associated increase in viscosity) of such resin systems may typically only comprise a few minutes. Undoubtedly, an installation not completed prior to expiration of the resin pot life could result in a flawed composite structure surrounding the pipe and pipe anomaly.
In general, a tension exists between the technique of slow and cumbersome pre-wetting and application of the fiber, layer-by-layer, versus the relatively hasty formation of the viscous resin structure due to expiration of the resin pot life and associated increase in viscosity. Thus, in pipe composite repair, many fiber and resin systems are difficult to mold and shape into the appropriate composite structure that overlay the pipe and pipe anomaly.
Moreover, there is a need in the industry for composite repair systems having relatively elevated glass transition temperature (Tg) and heat deflection temperature (HDT). Such a need may exist because of relatively high temperature environments and contents of the pipeline, temperature and pressure ratings of the pipeline, requirements of industry standards, and so forth. An example of an applicable industry standard is the American Society of Mechanical Engineers (ASME) Post-Construction Code-2 (PCC-2) entitled “Non-Metallic Composite Repairs Systems for Piping and Pipe Work.” In certification within the ASME PCC-2, for example, the resin/fiber composite system generally should meet certain Tg and HDT requirements. According to ASME PCC-2, for example, the service temperature of the repair systems are reported as the Tg minus 36° F./HDT minus 27° F. for non-leaking pipe work, and Tg minus 54° F./HDT minus 36° F. for leaking pipe work.
It should be noted that resins which advantageously cure at room temperature (e.g., certain epoxies, urethanes, polyesters, acrylics, vinyl esters, etc.) with low shrinkage and a realistic work time (e.g., less than 2 hours) may disadvantageously cure to a lower Tg (e.g., in the range of 110° F. to 135° F.) without a post cure (e.g., with an external heat source). Thus, typically, an ambient-temperature cure of a traditional resin may only give a Tg of 135° F. or less of the cured resin. Such a Tg would only satisfy an operating class of 99° F. for a non-leaking pipe per the ASME PCC-2 standard, which is unsatisfactory for many pipe repair applications. The option of adding an external heat source in the field to heat the curing resin (e.g., to 150° F. to 400° F.) for a period of hours is typically cumbersome, time consuming, impractical, and generally not cost effective for many field repairs of pipe work. This impractical procedure of external heating (post curing) may also substantially prohibit the use of heat curing/activated epoxy resin systems (and urethanes, epoxy-vinyl esters, vinyl esters, polyesters etc) that typically would provide a Tg of the cured resin over 200° F., but still generally need the application an external heat source over 150° F. to 400° F. for a period of hours for a proper cure.